Koeman hopes to raid his old club Southampton to land Dutch centre-back Van Dijk.

But Saints are reluctant to sell the 25-year-old stopper who is valued at £50million and also on Man City's radar.

Virgil van Dijk is Koeman's priority but he's aware he has rivals for his signature (Image: Julian Finney)

England and Burnley man Michael Keane is an alternative

It has forced Koeman to consider alternatives including Burnley defender Michael Keane, 23, and Boro's Gibson.

Gibson – Middlesbrough owner Steve Gibson's nephew — signed a new deal in August which runs until 2021. But the 23-year-old is now considered an England prospect and is on the radar of other big clubs.

He helped promoted Boro keep their sixth clean sheet this season against champions Leicester on Monday.